Camera tube convertible from integral mesh to separate mesh type

ABSTRACT

A camera tube has a wall anode and a mesh electrode which is separate from the wall anode. Connection is made to the mesh electrode from a terminal outside the tube envelope by means of two diammetrically opposed conductors which are connected to the wall anode by fuses which after completion of manufacture may be fused to convert the tube from one of the integral mesh type to one of the separate mesh type.

United States Patent 1191 Seholz CAMERA TUBE CONVERTIBLE FROM INTEGRAL MESH T0 SEPARATE MESH TYPE v Inventor: Hans Scholz, Essex, England Assignee: English Electric Valve Company Limited, Chelmsford, Essex, England Filed: Jan. 22, 1973 Appl. No.: 325,458

Foreign Application Priority Data I Feb. 17, 1972 Great Britain 7353/72 u.s. c1 315/3, 313/65 R, 29/2513 int gl .11011 29 96, H01 j 31/28, HO 1 j 29/02 [45] May 28, 1974 [58] Field of Search 313/65 R, 65 A,65 T; 315/3 Primary ExaminerRobert Segal Attorney, Agent, or Firm-Baldwin, Wight & Brown 5 7 ABSTRACT A camera tube has a wall anode and a mesh electrode which is separate from the wall anode. Connection is made to the mesh electrode from a terminal outside the tube envelopeby means of two diammetrically opposed conductors which are connected to the wall anode by fuses which after completion of manufacture may be fused to convert the tube from one of the integral mesh type to one of the separate mesh type.

4 Claims, 3 Drawing Figures I I CAMERA TUBE CONVERTIBLE FROM INTEGRAL MESH-I T SEPARATE MESH TYPE This invention relates to camera tubes and more specifically to camera tubes having a wall anode electrode connected to a terminal external of the tube envelope and a mesh electrode disposed in front of said wall anode electrode. An example of a camera tube of the above kind, and to which the present invention is particularly applicable, is a camera tube of the kind known under the Registered Trade Mark Leddicon.

A common arrangement for applying potential to the aforementioned mesh is to connect the mesh across the wall anode electrode, so that the potential applied thereto is that applied tothe wall anode electrode.

Such an arrangement is schematically illustrated in FIG. I of the accompanying drawing in which 1 represents the wall anode electrode 2 the mesh electrode connected thereacross so as to exhibit the same potential as the wall anode electrode and 3 is a terminal external of the tube envelope to which potential for the wall anode 1 and other electrode 2 may be applied. A tube thus arranged is usually referred to as an integral mesh type tube.

Where it is required torun the mesh electrode at a potential different from that of the wall anode electrode, it is common to provide two diametrically opposed conductors extending from the mesh electrode to a further terminal external of the tube envelope.

Such an arrangement is illustrated in FIG. 2 of the accompanying drawing, in which reference numberals 1, 2, and 3 refer to parts similarly referenced in FIG. 1. In this case, however, the mesh electrode 2 is separated from the wall anode electrode 1 and is connected to a further terminal 4 external of the tube envelope, by two diametrically opposed conductors 5 and 6. A tube so arranged is usually referred to as a separate mesh type tube.

In order to simplify manufacturing procedures, it has been proposed to construct only tubes of the separate mesh type, as shown in FIG. 2 and, where the characteristics of an integral mesh type tube are required, to provide an external connection between external terminals 3 and 4. However, the purpose of using the two diametrically opposed conductors 5 and 6 is, as is well known per se. to minimise the effect of so called line scan pick-up." This effect is a spurious signal generated in operation in the conductors 5 and 6 by the action of the scanning field. Using the diametrically opposed conductors 5 and 6, the tube can be rotated to a position where the pick-up induced in each conductors 5 and 6 is in opposition and tends to cancel out. If it is attempted to convert a separate mesh type tube to an integral mesh type tube by connecting terminals 3 and 4 together externally, it is found that pick-up in the conductors 5 and 6 removes the freedom, normally associated with an integral mesh type tube, to operate the tube in any orientation.

The present invention seeks to provide an improved camera tube of the kind referred to, which may be converted from a tube having characteristics of an integral mesh tube to one of the separate mesh type, whilst avoiding or reducing the aforementioned difficulty.

According to this invention a camera tube of the kind referred to is provided wherein the mesh electrode is separated from the wall anode electrode and has two substantially diametrically opposed conductors extending therefrom to afurther terminal, external of the tube envelope, fusible means, internal of the tube envelope, being provided electrically to connect said wall anode to said two diametrically opposed conductors, whereby the said camera tube, after completion of manufacture, may be converted from a tube exhibiting characteristics of the integral mesh type to a'separate mesh type by fusing said fusible means.

The aforementioned fusible means should be provided between the wall anode electrode and the said two conductors as close as possible to the mesh electrode.

Preferably, said fusible means comprises two thin strips of platinum, one extending between one of said conductors and the wall anode electrode and the other extending between the other of said two conductors and the wall anode electrode, whereby theaforementioned conversion of the said tube may be accomplished by passing a suitable current'between the said two terminals externally of the tube envelope.

Preferably again further fusible means is provided in at least one of said two conductors. Where said first mentioned fusible meanscomprises two platinum strips as above described and conversion is to be carried out by passing a current between said two external terminals said further fusible means is provided to have a current carrying capacity greater than that of the fusible strip between the wall anode and the conductor in which the further fusible means is provided. In this case where the tube is required to be one exhibiting the characteristics of an integral mesh type tube the further fusible means isfused by RP. heating or other convenient means after manufacture, whilst leaving the first mentioned fusible means intact.

The invention is further described with reference to and illustrated in FIG. 3 of the accompanying drawings in which again like references are used for like parts in FIGS. 1 and 2.

It will be noted that the tube illustrated in FIG. 3 is similar to the tube illustrated in FIG. 2 except for the provision of fusible thin platinum strips 7 and 8, between the wall anode 2 and conductors 5 and 6 respectively. In addition, a further fusible thin platinum strip 9 is included in the length of conductor 6. Fusible platinum strip 9 is provided to carry a heavier current than the fusible platinum'strip 8 to ensure that the strip 8 fuses before the strip 9, when a suitable current is passed between terminals 3 and 4.

In order to convert the tube from one as shown in FIG. 3 exhibiting the characteristics of an integral mesh type tube to one of the separate mesh type. A suitable current is passed between terminals 3 and 4 in order to fuse strips 7 and 8. Where the tube is required to be one exhibiting the characteristics of an integral mesh type tube strips 7 and 8 are left intact and strip 9 is fused by RF heating in order to break open the loop formed by the two conductors 5 and 6, which, since these conductors are still connected to mesh 2, might otherwise be responsible for a small amount of inductive pick-up.

I claim I. A camera tube including an evacuated envelope a wall anode within said envelope a mesh electrode disposedaxially in front of said wall anode and separate therefrom, two substantially diametrically opposed conductors electrically connected to said mesh electrode and extending axially therefrom and first and second terminal means external of the tube envelope connected through said envelope said first terminal means to said wall anode, and said second terminal means to said two conductors and wherein there is provided within said envelope fusible means electrically connecting said wall anode to at least one of said two diametrically opposed conductors to enable electrical isolation of said mesh electrode from the wall anode subsequent to manufacture.

2. A tube as claimed in claim 1 and wherein said fusible means comprises two thin strips of platinum, one extending between one of said conductors and the wall anode electrode and the other extending between the other of said two conductors and the wall anode electrode, whereby the aforementionedconversion of the said tube may be accomplished by passing a suitable the tube envelope.

. current between the said two terminals externally of 3. A tube as claimed in claim 1 and wherein further fusible means is provided in at least one of said two conductors.

4. A tube as claimed in claim 1 and wherein said fusible means comprises two thin strips of platinum, one extending between one of said conductors and the wall anode electrode and the other extending between the other of said two conductors and the wall anode electrode, whereby the aforementioned conversion of the said tube may be accomplished by passing a suitable current between the said two terminals externally of the tube envelope and wherein further fusible means is provided in at least one of said two conductors said further fusible means being provided to have a current carrying capacity greater than that of the fusible strip between the wall anode and the conductor in which the further fusible means is provided. 

1. A camera tube including an evacuated envelope a wall anode within said envelope a mesh electrode disposed axially in front of said wall anode and separate therefrom, two substantially diametrically opposed conductors electrically connected to said mesh electrode and extending axially therefrom and first and second terminal means external of the tube envelope connected through said envelope said first terminal means to said wall anode, and said second terminal means to said two conductors and wherein there is provided within said envelope fusible means electrically connecting said wall anode to at least one of said two diametrically opposed conductors to enable Electrical isolation of said mesh electrode from the wall anode subsequent to manufacture.
 2. A tube as claimed in claim 1 and wherein said fusible means comprises two thin strips of platinum, one extending between one of said conductors and the wall anode electrode and the other extending between the other of said two conductors and the wall anode electrode, whereby the aforementioned conversion of the said tube may be accomplished by passing a suitable current between the said two terminals externally of the tube envelope.
 3. A tube as claimed in claim 1 and wherein further fusible means is provided in at least one of said two conductors.
 4. A tube as claimed in claim 1 and wherein said fusible means comprises two thin strips of platinum, one extending between one of said conductors and the wall anode electrode and the other extending between the other of said two conductors and the wall anode electrode, whereby the aforementioned conversion of the said tube may be accomplished by passing a suitable current between the said two terminals externally of the tube envelope and wherein further fusible means is provided in at least one of said two conductors said further fusible means being provided to have a current carrying capacity greater than that of the fusible strip between the wall anode and the conductor in which the further fusible means is provided. 